nary mirror, d, but one of graduated opacity. This may be produced by removing the silvering from the glass in lines; or, if the glass be silvered by chemical deposition, causing the silver to be deposited upon it in lines, somewhat as represented by Fig. 63. Near one side of the glass the lines are made fine and open, and progressively in passing toward the other side they become bolder and closer until a completely-silvered surface is reached. Other means for obtaining a graduated opacity and reflecting power may be resorted to.
"By passing such a graduated mirror between the object at c² and the audience, the object may be made to fade from the sight, or gradually to resolve itself into another form."
Hopkins in his fine work on "Magic, stage illusions, etc.," thus describes one of the many effects which can be produced by the Blue Room apparatus. The curtain rises, showing "the stage set as an artist's studio. Through the centre of the rear drop scene is seen a small chamber in which is a suit of armor standing upright. The floor of this apartment is raised above the level of the stage and is approached by a short flight of steps. When the curtain is raised a servant makes his appearance and begins to dust and
